import pandas as pd

# create a dataframe
df = pd.DataFrame({'id': [1, 2, 3, 4, 5],
                   'name': ['Alice', 'Bob', 'Charlie', 'Dave', 'Eve'],
                   'age': [25, 30, 35, 40, 45]})

# create a new column with the combined values of the id and name columns
df = df.assign(id_name=df['id'].astype(str) + '_' + df['name'])

# set the id_name column as the primary key index
df.set_index('id_name', inplace=True)

# display the dataframe with the new primary key index
print(df)